The key to further progress lies in the chain of 1/~1 cells marked with "*"s in this grid. We can see that r7c5 cannot be a "1" because if it is a contradiction cannot be avoided. So the "1" in row 7 must appear at r7c9, and the rest of the puzzle is easily resolved.

This formation is a type of "turbot fish," which has been well analyzed by "Nick70" on the sudoku.com forum. dcb